chore(deps): bump squidfunk/mkdocs-material in /docs

Bumps squidfunk/mkdocs-material from `6b124e1` to `521644b`.

---
updated-dependencies:
- dependency-name: squidfunk/mkdocs-material
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/Dockerfile

@@ -1,5 +1,5 @@
 # v9.1.18
-FROM squidfunk/mkdocs-material@sha256:6b124e13728a591607e0f087920763e405fc18861736a997896d0b253867a7b7
+FROM squidfunk/mkdocs-material@sha256:521644b58bc0c806083ef66e8b1027861bd3e98c433b251c436c5c0cc7733603
 # pip-compile --generate-hashes --output-file=requirements.txt requirements.in
 COPY requirements.txt /tmp/
 RUN pip install --require-hashes -r /tmp/requirements.txt